1. Field of the Invention
The present invention relates to a signal amplifying circuit and a signal amplifying method, and more particularly, to a low noise amplifier (LNA) with a lower noise figure and related method thereof.
2. Description of the Prior Art
In a wireless receiving system, a low noise amplifier is utilized to amplify a received wireless signal to generate a received signal. To make sure that the wireless receiving system extracts the data from the received signal accurately, the low noise amplifier should not introduce too much noise to the received signal such that the data in the received signal is prevented from being affected by the noise. In other words, the noise figure of the low noise amplifier should be low enough, thus ensuring the accuracy of the data in the received signal. Generally speaking, the noise figure of the low noise amplifier is affiliated with the field effect transistors used in the low noise amplifier. Specifically, the noise figure of the low noise amplifier is proportional to the channel noise coefficient and the gate noise coefficient of the field effect transistors, and the noise figure of the low noise amplifier is inversely proportional to the operating cutoff frequency of the field effect transistors. To put it another way, the wireless received signal would be affected by the noise of the field effect transistors so long as the low noise amplifier is composed of field effect transistors. Therefore, how to improve the noise figure of a low noise amplifier using a low-cost solution has become an issue in the pertinent field.